Earliest historical evidence from Mehargarh  (north-west India) shows beginning of civilization in India at around 6500 B.C. It is the earliest and largest urban site of the period in the world. This site has yielded evidence for the earliest domestication of animals, evolution of agriculture, as well as arts and crafts. The horse was first domesticated here in 6500 B.C. The people in this tradition are the same basic ethnic groups as in India today, with their same basic types of languages Indo-European and Dravidian. There is a progressive process of the domestication of animals, particularly cattle, the development of agriculture, beginning with barley and then later wheat and rice, and the use of metal, beginning with copper and culminating in iron, along with the development villages and towns.

Two important cities were discovered: Harappa on the Ravi river, and Mohenjodaro on the Indus during excavations in 1920. The remains of these two cities were part of a large civilization and well developed ancient civilization, which is now called by historians as 'Indus Valley Civilization', or 'Saraswati Civilization'. Later Harappan (Sarasvati) civilization 3100-1900 BC shows massive cities, complex agriculture and metallurgy, sophistication of arts and crafts, and precision in weights and measures. They built large buildings, which were mathematically-planned. The city planning in those ancient cities is comparable to the best of our modern cities. This civilization had a written language and was highly sophisticated.  Some of these towns were almost three miles in diameter with thousands of residents. These ancient municipalities had granaries, citadels, and even household toilets. In Mohenjodaro, a mile-long canal connected the city to the sea, and trading ships sailed as far as Mesopotamia. At its height, the Indus civilization extended over half a million square miles across the Indus river valley, and though it existed at the same time as the ancient civilizations of Egypt and Sumer, it far outlasted them. This Sarasvati civilization was a center of trading and for the diffusion of civilization throughout south and west Asia, which often dominated the Mesopotamian region. 
Mehrgarh, Harappa, Mohenjodaro, Kalibangan and Lothal are peripheral cities of the great Sarasvati civilization with more than 500 sites along its banks awaiting excavation.

Golden period of Indian History -

The Mauryan Empire :

Although Indian accounts to a large extent ignored Alexander the Great's Indus campaign in 326 B.C., Greek writers recorded their impressions of the general conditions prevailing in South Asia during this period. A two-way cultural fusion between several Indo-Greek elements-especially in art, architecture, and coinage--occurred in the next several hundred years. North India's political landscape was transformed by the emergence of Magadha in the eastern Indo-Gangetic Plain.

As the overextended Hellenistic sphere declined, a king known as Chandragupta swept back through the country from Magadha (Bihar) and conquered his way well into Afghanistan. This was the beginning of one India's greatest dynasties, the Maurya. In 322 B.C., Magadha, under the rule of Chandragupta Maurya, began to assert its hegemony over neighboring areas. Chandragupta, who ruled from 324 to 301 B.C., was the architect of the first Indian imperial power-the Mauryan Empire (326-184 B.C.)--whose capital was Pataliputra, near modern-day Patna, in Bihar.